The three areas that matter
Tableau Desktop looks busy, but almost everything you do happens in three places. The Data pane on the left lists every field from your data source. The shelves across the top — Columns and Rows — decide the structure of your view. The Marks card controls how each mark looks: its type, colour, size, label, and tooltip.
Everything else (the Analytics pane, the Pages shelf, the Filters shelf) is a refinement on top of those three.
Rows, Columns, and what a "view" is
Dropping a field on Columns spreads data horizontally; dropping it on Rows stacks it vertically. That's the whole grammar. A bar chart is a dimension on one axis and a measure on the other. Swap them and the bars turn from vertical to horizontal.
Tableau calls the result a view, and a sheet holds exactly one view. You combine multiple sheets into a dashboard later.
The Marks card
The Marks card is where a plain chart becomes a readable one. The dropdown at the top sets the mark type — bar, line, square, circle, map, text, and so on — or leave it on Automatic and let Tableau choose.
Below that are the property targets. Drop a dimension on Colour to split marks into a colour legend. Drop a measure on Size to scale them. Label prints values on the marks; Detail adds granularity without changing appearance; Tooltip controls the hover text.
Show Me
Show Me, top right, suggests chart types based on the fields you've selected. It's a good way to learn what's possible early on, but it makes layout decisions for you. Once you know what you want, building manually gives you more control.